Contact mechanism for electronic overload relays

ABSTRACT

Ease of assembly, inexpensive construction and improved reliability may be achieved in a trip mechanism for an overload relay including a housing containing a bistable armature mounted in the housing on a pivot for pivotal movement between two stable positions. Fixed contacts are located within the housing and moveable contacts are carried by leaf springs for movement to a closed position with the fixed contacts for one of the two stable positions and for movement to an open position relative to the fixed contacts for the other of the two stable positions. Projections carried by the armature are operative to move the leaf springs and their associated contacts. A latch arm is carried by the armature and has a latch surface. A spring is mounted on the housing and has a latch finger for engaging the latch surface and retaining the armature in one of the two positions.

FIELD OF THE INVENTION

This invention relates to electrical relays, and more particularly, to atrip mechanism for an overload relay.

BACKGROUND OF THE INVENTION

Overload relays are electrical switches typically employed in industrialsettings to protect electrical equipment from damage due to overheatingin turn caused by excessive current flow. In a typical case, theelectrical equipment is a three-phase motor which is connected to apower source through another relay commonly referred to as a contactor.A typical contactor is a heavy duty relay having three switched powerpaths for making and breaking each of the circuits connected to thethree phase power source. The motion required to make and break thecontacts is provided magnetically as a result of current flow through acoil which in turn is energized by a current whose flow is controlled byanother switch, typically remotely located.

In a conventional setup, an overload relay is connected in series withthe control switch for the coil of the contactor. When an overloadcondition is detected by the overload relay, the same cuts off power tothe coil of the contactor, allowing the contactor to open and disconnectthe electrical equipment that is controlled by the contactor from thesource of power to prevent injury to the electrical equipment.

In the past, overload relays have utilized resistive heaters for eachphase which are in heat transfer relation with a bimetallic elementwhich in turn controls a switch. When an overload is sensed as, forexample, when there is sufficient heat input from the resistive heaterto the bimetallic element, the bimetallic element opens its associatedswitch to de-energize the contactor coil and disconnect the associatedpiece of electrical equipment from the source of power.

More recently, the resistive heater-bi-metallic element type of relayhas been supplanted by electronic overload relays. See, for example,commonly assigned U.S. Pat. No. 5,179,495 issued Jan. 12, 1993, toZuzuly, the entire disclosure of which is herein incorporated byreference. Outputs of such circuitry typically are relatively lowpowered and as a consequence, in order for the output to control thecontactor coil current, a solid state switch may be required. The solidstate switch may, in turn, control flow to a relatively low powercontact mechanism which in turn is operable to control the flow ofcurrent to the contactor as well as to operate an indicator. In theusual case, the indicator will be a light which will be illuminated uponthe occurrence of a disconnect resulting from an overload. One suchcontact mechanism is disclosed in my commonly assigned copendingapplication entitled, "Trip Mechanism for an Overload Relay", Ser. No.08/838,904, Filed Apr. 11, 1997, the entire disclosure of which isherein incorporated by reference.

The mechanism therein disclosed works extremely well for its intendedpurpose. However, because the same uses so-called "bridging" contacts,assembly is somewhat more difficult, increasing its cost. Moreover,bridging contacts may pose reliability problems when a circuit is to bemade (as opposed to broken), particularly at low currents or loads thatare associated with solid state devices. Specifically, in a bridgingcontact, two spaced fixed contacts are employed along with a moveablecontact bar. The contact bar must make good electrical contact with bothof the fixed contacts in order to complete a circuit with theconsequence that if either contact is deteriorated as a result of arcingor the like, or if grime enters the switching mechanism, the circuitcannot be made. Because two contacts are involved, the likelihood offailure may be as much as doubled over the situation where only onecontact is employed.

The present invention is directed to overcoming one or more of the aboveproblems.

SUMMARY OF THE INVENTION

It is the principal object of the invention to provide a new andimproved trip mechanism for an overload relay. More specifically, it isan object of the invention to provide an improved trip mechanism for anoverload relay that is easier and more economical to assemble and whichhas improved reliability.

An exemplary embodiment of the invention achieves the foregoing objectin a trip mechanism for an overload relay that includes a housing, abistable armature mounted in the housing on a pivot for pivotal movementbetween two stable positions, and fixed contacts within the housing.Moveable contacts carried by leaf springs are provided for movement to aclosed position with the fixed contacts for one of the two stablepositions and for movement to an open position relative to the fixedcontacts for the other of the two stable positions. The leaf springs arepositioned to be engaged by the armature. A latch surface is carried byone of the armature and the housing and a spring is mounted on the otherof the armature and the housing and has a latch finger for engaging thelatch surface and retaining the armature in one of the two positions.

In a preferred embodiment, the leaf springs are spaced from one anotherand are on opposite sides of the pivot. The armature includes at leasttwo projections, one on each side of the pivot, for engaging acorresponding one of the leaf springs.

In a preferred embodiment, the leaf springs have fixed ends secured tothe housing and moveable ends carrying the moveable contacts. Themoveable ends are bifurcated to define two contact fingers and there isone of the moveable contacts on each of the fingers.

According to another aspect of the invention, there is provided a tripmechanism for an overload relay which includes a housing, and a bistablearmature mounted in the housing on a pivot for pivotal movement betweentwo stable positions. Fixed contacts are located within the housing anda pair of leaf springs are provided, each having one end secured to thehousing and an opposite free end. Moveable contacts are carried by thefree ends of the leaf springs for movement to a closed position with thefixed contacts for one of the two stable positions and for movement toan open position relative to the fixed contacts for the other of the twostable positions. Actuators are mounted on and moveable with thearmature for engaging a corresponding one of the leaf springs and alatch arm is carried by the armature and has a latch surface. A torsionspring is mounted on the housing and has a latch finger for engaging thelatch surface and retaining the armature in one of the two positions. Apush button is reciprocally mounted in the housing for movement into andout of engagement with the latch finger. The push button when pushedinto engagement with the latch finger, dislodges the latch finger fromthe latch surface to release the latch arm.

Additional objects and advantages of the invention will be set forth inthe description which follows and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate a presently preferred embodimentof the invention and, together with the general description given aboveand a detailed description of the preferred embodiment given below,serve to explain the principles of the invention.

FIG. 1 is a somewhat schematic, sectional view of a trip mechanism madeaccording to the invention showing the configuration of the componentsin an automatic reset position; and

FIG. 2 is a fragmentary plan view of a preferred form of a set ofcontacts used in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, the overload relay as shown in a resetposition, specifically, an auto-reset position, and includes a housing,generally designated 10, shown fragmentarily. Mounted within the housingis a first set of normally open, fixed contacts, generally designated12, and a set of normally closed, fixed contacts, generally designated14. The housing includes a pivot pin 16 upon which an elongated,bistable armature, generally designated 18 is pivoted. The armature isshown in one of its stable positions and is operative to maintain afirst set of moveable contacts, generally designated 20, in an openposition. In its other bistable position, the armature 18 is operativeto open a second set of moveable contacts, generally designated 22,which are normally closed. The contacts 20 and 22 make and break withthe fixed contacts 12 and 14, respectively.

A latch lever, generally designated 24, is connected to the armature tobe moveable therewith and thus will rock about the pivot 16 between thetwo stable positions of the armature 18.

The housing includes an opening 25 which reciprocally receives a manualoperator, generally designated 26, which includes a push button surface28 and a depending shank 30. The push button 28 is mounted for movementgenerally toward and away from the latch lever 24. Turning to themoveable contacts 20,22, their constructions are generally identical andeach includes an elongated leaf spring 32 having one end 34 mounted to ahousing part 36 and a free end 38. The free end, in one embodiment ofthe invention, and as shown in FIG. 2, is bifurcated as at 42 to definetwo contact fingers, 44 and 46. Each of the contact fingers carries acontact 48 which closes against the corresponding contact or set offixed contacts 12,14 as the case may be. In the usual case, normallyopen contacts 12,20 are operative to provide power to an indicator, suchas an electrical light, to illuminate the same when the relay has beentripped. On the other hand, the normally closed contacts 14,22 arenormally employed to provide electrical power to the coil of a contactorto energize the same to in turn provide electrical power to the piece ofequipment, typically a motor, being controlled. While the leaf spring 32need not be bifurcated at its free end 38 and thus may mount but asingle one of the contacts 48, the bifurcated construction is preferredsince only one of the contacts 48 on a given one of the leaf springs 34need make contact with the associated fixed contact 12,14 to make anelectrical circuit. As a consequence, if one of the contacts becomescorroded or is fouled as by environmental grime, the circuit can stillbe made by the other contact, providing improved reliability.

It will also be appreciated that use of a leaf spring contactconstruction reduces the number of components that are required in eachset of contact 12,20; 14,22 providing for easier assembly and a moreeconomical construction than would be the case if bridging contacts wereused.

The armature 18 carries two projections 50,52, one on each side of thepivot 16. The projection 50 is adapted to engage the leaf spring 32associated with the contacts 12,20 to open the same while the projection52 is operable to engage the leaf spring 32 engageable with the contacts14,22 to open them as well.

The armature 18 includes a first magnetic pole piece 62 and a parallel,spaced second pole piece 64. Pole pieces 62 and 64 sandwich the pivot 16as well as two permanent magnets 66. The two permanent magnets 66 couldbe combined into a unitary structure if desired but for convenience, toaccommodate the pivot, two of the magnets 66 are employed.

The housing mounts a magnetic yoke or pole piece 70 which is in the formof a shallow "U" having legs 72 and 74. A coil 76 is disposed about thebight of the pole piece 70. In some cases, the coil 76 will be definedby a single coil while in other cases, two electrically separate coilswill be wound thereon, one on top of the other. The particulararrangement depends upon the control mode of the electronic circuitryemployed. If the same reverses current flow through the coil 76 toswitch the relay from one state to the other, only a single coil need beused. On the other hand, if the electrical circuit does not reversecurrent flow, but rather switches it from one coil to the other, thentwo coils, oppositely wound from one another, will be employed as thecoil 76.

Turning now to the latch lever 24, the same is moveable within thehousing 10 with the armature 18 between two bi-stable positions as notedpreviously. One position is that shown in FIG. 1 while another positionwill have the projection 52 opening the electrical contacts 14,22 andallowing the contacts 12,20 to close.

The latch lever 24, at its upper end, includes an elongated notch 82which underlies an opening (not shown) in the housing 10. A tool, suchas the tip of a screwdriver, can be fitted through the opening andinserted in the notch 82 to apply a manual force to the lever 24 toshift it between the two stable positions for manual test purposes.

Just below the notch 82, a latch surface defined by two adjoiningsurfaces 84,86 is provided. Underlying the latch surface 84,86 is aspring latching finger 88 having an upturned end 90 which is adapted toembrace and latch against the surface 86 of the latch surface 84,86under certain conditions to be described. The latch finger 88 extendsfrom the coil 92 of a torsion spring, generally designated 94, which ismounted on a post 96 within a pocket within the housing 10.Alternatively, the spring 94 may be mounted on the latch lever 24 andthe latch surface 84,86 on the housing 10.

The end 98 of the coil 92 opposite the latch finger 88 is abuttedagainst the housing 10 to prevent rotation of the coil 92 on the post96. The latch finger may latch the latch lever in one of the two stablepositions of the armature 18, such position being the one not shown inFIG. 1.

The latch lever 24 also carries a flat, diagonal projection 100 closelyadjacent to a post 102 which is generally parallel to the pivot 16. Asecond torsion spring, generally designated 104, is mounted on the post102 and includes one end 106 fixed to the projection 100 to preventrotation of the coil 108 of the torsion spring 104 about the post 102.The opposite end 110 of the torsion spring 104 acts as a reset fingerand extends diagonally, at an acute angle past the end of the projection100 in the direction of the push button actuator 26. In this connection,the shank 30 of the push button actuator 26 includes a notch 112 whichacts as a stop surface and cooperates with the reset finger 110 forshifting the latch 24 from a tripped position, that is, the position notshown in FIG. 1, to the reset position illustrated in FIG. 1.

Turning now to the push button 26 actuator, and specifically the shank30, the lower end includes a ledge 114 against which a biasing spring116 is abutted. The biasing spring 116 provides an upward bias to thepush button 26 to bias the same upwardly from the position shown in FIG.1.

Just above the shank 30, the operator 26 includes an outwardly extendingtongue or ledge or 120. At the same time, the housing 10 includes afirst notch having a retaining surface 122 and a second notch having adetent surface 124. In its full uppermost position, the ledge 120 of thepush button actuator 26 abuts the notch 122 and is retained within thehousing 10 thereby.

Preferably, the operator 26 is of generally cylindrical cross sectionexcept for the ledge 120 so as to be rotatable within the housing 10 aswell as reciprocal therein. As a consequence, when the operator ispushed downwardly to the position illustrated in FIG. 1, the same may berotated to bring the ledge 120 into underlying relation with the detentsurface 124. In this position, the operator is retrained in itslowermost position which corresponds to the automatic reset mode shownin FIG. 1.

It is to be particularly observed that in the automatic reset mode, theledge 120 abuts the upper end 90 of the latch finger 88. As seen in FIG.1, this holds the latch finger 88 out of engagement with the latchsurface 84,86 on the latch arm 24. However, if the push button 28 isrotated to bring the ledge 120 out of engagement with the detent surface24 and allowed to move upwardly within the housing 10 as a result of thebias of the spring 116, the upper end 90 of the latch finger 88 willrest against the surface 84. If the relay is tripped, the armature 18will be caused to move to its other bistable position (the one not shownin FIG. 1) with a consequence that the spring finger 88 will be cammedalong the surface 84 to ultimately lodge behind the latch surface 86 andhold the latch lever 24 in its tripped position.

To reset the relay, the push button, assuming its in its uppermostposition, is pushed downwardly. When the ledge 120 encounters the upperend 90 of the spring finger 88, the spring finger 88 will be moved outof engagement with the latching surface 86. At the same time, the end110 of the spring 104 will have lodged in the notch 112 and furtherdownward movement of the push button 26 will cause the end 110 of thespring 104 to move toward the horizontal position, simultaneouslydriving the latch lever 24 to the position illustrated in FIG. 1.

Other structural and operational features of the mechanism may beascertained by reference to my previously identified co-pendingapplication.

From the foregoing, it will be appreciated that an overload relay madeaccording to the invention, by reason of the use of the leaf springs 32carrying the contacts 48 is significantly easier to assemble and moreeconomical. It is also more reliable in that it includes fewer partsthan a bridging contact type of mechanism. That reliability may befurther enhanced through the use of a bifurcated free end 38 on each ofthe leaf springs, to define two contact fingers 44,46, each carrying oneof the contacts 48.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspect isnot limited to the specific details, and representative devices, shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

I claim:
 1. A trip mechanism for an overload relay comprising:a housing;a bistable armature mounted in said housing on a pivot for pivotalmovement between two stable positions; fixed contacts within saidhousing; moveable contacts carried by leaf springs for movement to aclosed position with said fixed contacts for one of said two stablepositions and for movement to an open position relative to said fixedcontacts for the other of said two stable positions, said leaf springsbeing positioned to be engaged by said armature; a latch arm carried byone of said armature and said housing and having a latch surfacethereon; and a spring mounted on the other of said armature and saidhousing and having a latch finger for engaging said latch surface andretaining said armature in one of said two positions.
 2. The tripmechanism of claim 1 wherein said leaf springs are spaced from oneanother and on opposite sides of said pivot; and said armature includesat least two projections, one on each side of said pivot for engaging acorresponding one of said leaf springs.
 3. The trip mechanism of claim 2wherein said leaf springs have fixed ends secured to said housing andmoveable ends carrying said moveable contacts; said moveable ends arebifurcated to define two contact fingers; and there is one of saidmoveable contacts on each of said fingers.
 4. The trip mechanism ofclaim 1 wherein said leaf springs have fixed ends secured to saidhousing and moveable ends carrying said moveable contacts; said moveableends are bifurcated to define two contact fingers; and there is one ofsaid moveable contacts on each of said fingers.
 5. A trip mechanism foran overload relay comprising:a housing; a bistable armature mounted insaid housing on a pivot for pivotal movement between two stablepositions; fixed contacts within said housing; a pair of leaf springseach having one end secured to said housing and an opposite free end;movable contacts carried by said free ends for movement to a closedposition with said fixed contacts for one of said two stable positionsand for movement to an open position relative to said fixed contacts forthe other of said two stable positions; projections mounted on andmoveable with said armature for engaging a corresponding one of saidleaf springs; a latch arm carried by said armature and having a latchsurface thereon; a torsion spring mounted on said housing and having alatch finger for engaging said latch surface and retaining said armaturein one of said two positions; and a push button reciprocally mounted insaid housing for movement into and out of engagement with said latchfinger, said push button, when pushed into engagement with said latchfinger dislodging said latch finger from said latch surface to releasesaid latch arm.
 6. A trip mechanism for an overload relay comprising:ahousing; an armature mounted for movement in said housing between twopositions; fixed contacts in said housing; a pair of leaf springs inspaced relation within said housing and each having a fixed end securedto said housing and a moveable free end; moveable contacts carried bysaid free ends for movement toward and away from said fixed contacts;means on said armature for engaging said leaf springs having a spring atlocations spaced from said fixed ends when said armature moves betweensaid positions; a moveable lever associated with said armature andoperable to shift said armature from at least one of said two positionsto the other of said two positions; an operator for said lever includingan element moveable toward and away from said lever; a spring fingercarried by one of said lever and said operator and extending at an acuteangle therefrom toward the other of said lever and said operator; and astop surface on the other of said lever and said operator positioned tobe engaged by said spring finger when said armature is in said oneposition and said operator is moved toward said lever and to disengageand release said spring finger when said armature has moved to the otherof said two positions.
 7. The trip mechanism of claim 6 wherein saidspring is a torsion spring having a coil mounted on a post and saidspring finger extends from said coil.
 8. The trip mechanism of claim 7wherein said post is on said lever and said stop surface is on saidoperator.
 9. The trip mechanism of claim 8 wherein said operator is amanual operator.
 10. The trip mechanism of claim 6 wherein said freeends are bifurcated to define two contact mounting fingers; one of saidmoveable contacts being disposed on each of said contact mountingfingers; said fixed contact being in pairs with the fixed contacts ofeach pair being positioned to be engaged by respective ones of themoveable contacts on respective bifurcated free ends of respective leafsprings.